Signals from the Nile River
Alexander Ruzmaikin [Alexander.Ruzmaikin@jpl.nasa.gov], Jet Propulsion Laboratory, California Institute of Technology, Pasadena.The major mode of the North Hemisphere variability (the North Annular Mode) is influenced by solar variability (Ruzmaikin and Feynman, J. Geophys. Res., 107, 2002). Because the north Nile River basin is covered by the spatial pattern of this mode, it is possible that the solar variability may be seen in the Nile River records. It is also known that North Atlantic affects the rainfall over North Africa and the Middle East. Water levels of the Nile River were critically important for agriculture in Egypt. Accurate (annual) records are available for 622-1470 A.D. and more sparse records since 1471 until 1922. These time series are not stationary thus hampering the application of standard spectral methods. We apply a new technique called Empirical Mode Decomposition, which is especially designed to deal with non-stationary, nonlinear time series (Huang et al., Proc. Roy. Soc. Lond. A 465, 903, 1998). Among the characteristic time scales found, there is one close to 11 years and one exceeding 200 years. We investigate the relationships between the North Hemisphere variability and the Nile River basin variability to find out whether these time scales are related to solar variability (to the solar cycle and Grand Minima of solar activity).